Automation devices have a plurality of communication layers, for example a data bus as one layer, a communication system as a next higher layer, above that an application layer, and an operating system as the highest layer. Today's communication systems often allow to synchronize a plurality of communication subscribers with one another. Such communication is known from document EP 2 110 754 A1, for example, which proposes a method for synchronizing bus users as the communication subscribers of an open automation system.
Synchronization of communication subscribers may, for example, be implemented according to the IEEE 1588 standard, and often a synchronization in form of a so-called clock-synchronized or isochronous synchronization is employed. In isochronous synchronization, a local clock system or a plurality of local clock systems of communication subscribers is matched and thus synchronized. This means that after synchronization all communication subscribers have the same time base. Further timing required for synchronous communication can be derived from this time base.
In automation devices with synchronized communication subscribers, collisions in terms of communication may occur. One reason for this may be such applications as motion control, for example. Such motion control requires both short cycle times of the application and short cycle times of the communication system. Advantageously, both systems, the application system and the communication system are additionally synchronized with each other. If such synchronization is lacking, jitter may increase, which may degrade overall system performance. Jitter refers to interferences which cause a slight variation in accuracy of the transmission clock, and such jitter is noticeable as a clock jittering over time during the transmission of digital signals. Jitter may arise despite of a synchronization between application system and communication system, since with a real-time operating system in an automation device preferably an interrupt is used to establish such synchronization. In that case, mutual interference of interrupts may occur.
Thus, there is a need for an automation device and method in which the occurrence of jitter is further reduced.